MMAP是一个内置的功能？ [英] Is mmap a built in function?

问题描述

我知道的 MMAP 的是一个系统调用，但必须在glibc的一些包装，做系统调用。然而，当我尝试使用的 GDB 的步骤通过的 MMAP 的在我的程序功能，的 GDB 的忽略它，因为它找不到任何的源文件它（注意：我从源代码编译我自己的glibc）。我可以通过其他的glibc库函数步骤等的的printf 和的malloc 的而不是 MMAP 的。我也使用该标志的 -fno-内置的让GCC不使用内置的功能。任何帮助将大大AP preciated。

I know that mmap is a system call, but there must be some wrapper in glibc that does the system call. Yet when I try to use gdb to step through the mmap function in my program, gdb ignores it as it can't find any source file for it (Note I compile my own glibc from source). I can step through other glibc library functions such as printf and malloc but not mmap. I also use the flag -fno-builtin so that gcc doesn't use built in functions. Any help on this will be greatly appreciated.

推荐答案

我不知道你的问题是什么。它完美对我很好。

I don't know what your problem is. It works perfectly fine for me.

使用系统 libc.so.6的，安装调试符号：

Using system libc.so.6, with debug symbols installed:

// mmap.c
#include <sys/mman.h>

int main()
{
  void *p = mmap(0, 4096, PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  return 0;
}

gcc -g mmap.c


$ gdb -q a.out
Reading symbols from /tmp/a.out...done.
(gdb) start
Temporary breakpoint 1 at 0x40052c: file mmap.c, line 5.

Temporary breakpoint 1, main () at mmap.c:5
5         void *p = mmap(0, 4096, PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
(gdb) step
mmap64 () at ../sysdeps/unix/syscall-template.S:82
82      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) 
mmap64 () at ../sysdeps/unix/syscall-template.S:83
83      in ../sysdeps/unix/syscall-template.S
(gdb) 
main () at mmap.c:6
6         return 0;
(gdb) q

使用我自己的glibc编译：

Using my own glibc build:

gdb -q a.out
Reading symbols from /tmp/a.out...done.
(gdb) start
Temporary breakpoint 1 at 0x40056c: file mmap.c, line 5.
warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?

Temporary breakpoint 1, main () at mmap.c:5
5         void *p = mmap(0, 4096, PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
(gdb) step
mmap64 () at ../sysdeps/unix/syscall-template.S:81
81      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) 
mmap64 () at ../sysdeps/unix/syscall-template.S:82
82              ret
(gdb) 
main () at mmap.c:6
6         return 0;
(gdb) q

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